[supersport#69]

I can’t tell if my engine is making a noise inside or some other outside noise causing it.
When I first start it it’s quiet. After a few minutes of warming up I hear a faint sound but I can’t pinpoint what it is. I
I took it to my mechanic and he can hear it but also can’t figure it out. He listened through stereoscope and can’t identify it.
There’s good oil pressure, the noise doesn’t get louder when you rev it, you have to put your ear close to even hear it, He said it’s not knocking or something major in his opinion.

What are some things I should look out or listen for to make sure it is nothing big?